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Here's a problem to work at with your graphic calculator or graph-plotting package on a computer.
If you plot the following lines
$\begin{eqnarray} y &=& 2x + 1\\ y &=& 2x + 4 \\ y &=& -0.5x + 1\\ y &=& -0.5x + 2.5 \end{eqnarray}$ |
the lines will enclose a square.
Can you find other sets of sloping lines that enclose a square?
If you are given the equations of two parallel lines